Top 3 Systems for Fatty Acid Synthesis

The following points highlight the top three systems for fatty acid synthesis. The systems are: 1. Mitochondrial System 2. Microsomal System for Chain Elongation 3. Extra Mitochondrial System for De NOVO Synthesis.

Fatty Acid Synthesis System # 1. Mitochondrial System:

a. Mitochondria catalyze the incorporation of acetyl-CoA into long chain fatty acids under anaerobic conditions.

b. The enzymes are mostly the same as those involved in P-oxidation excepting α, β-un- saturated acyl-CoA reductase which con­verts α, β-unsaturated acyl-CoA to a satu­rated compound, requiring NADPH + H⁺

c. Pyridoxal phosphate (B₆ – PO₄) as a  coen­zyme is required for the enzyme condens­ing acetyl-CoA with acyl-CoA; thus, thiolase is not used in this synthetic path­way.

d. Since this system takes place under anaerobic condition the physiologic sig­nificance of this pathway is uncertain.

Fatty Acid Synthesis System # 2. Microsomal System for Chain Elongation:

a. This is the main pathway for the elonga­tion of existing fatty acid molecules.

b. Acyl-CoA compounds are converted to higher fatty acids by means of malonyl-CoA along with NADPH + H⁺. The acyl groups include the saturated series from C₁₀ – C₁₆ as well as some unsaturated C₁₈ fatty acids.

c. Fasting prevents chain elongation.

Fatty Acid Synthesis System # 3. Extra Mitochondrial System for De NOVO Synthesis:

De novo synthesis of palmitic acid from acetyl-CoA is carried out in the cytoplasm by fatty acid synthase (multi enzyme complex). This mainly takes place in liver, kidney, lactating mammary gland, brain etc.